a. Field of the Invention
The invention relates generally to ultrasonic detectors and, more particularly, to portable ultrasonic detectors used to detect the condition of motor bearings and/or arcing in electrical cabinets at widely separated locations.
b. Description of the Related Art
Ultrasonic sensors have been used to detect ultrasonic energy generated by friction within mechanical devices, such as that created by worn bearings, as disclosed in U.S. Pat. No. Re. 33,977 to Goodman, et al., the contents of which are hereby incorporated herein by reference in their entirety. The greater the amount of friction, the greater is the intensity of the generated ultrasonic energy. Applying a lubricant to the device reduces friction and consequently the intensity of the generated ultrasound drops. Measuring ultrasonic energy thus provides a way to determine when lubrication has reached the friction generating surfaces. Additionally, faulty devices, such as bearings, generate a higher level of ultrasonic energy than do good bearings and thus, this condition can also be detected.
In the past decisions have been made on when to lubricate bearings based on the amount of time that has passed since the last application of lubricant and the specific amount of lubricant added at that time. Typically this information was compared to manufacturer's recommendations. However, a major reason for bearing failure is improper lubrication, not just a failure to lubricate. In particular, over lubrication can be a problem. It is known in the art to combine a lubrication tool with an ultrasonic detector to help control the application of lubricant to bearings. Such devices are disclosed in U.S. Pat. No. 6,122,966 and No. 6,339,961 of Goodman et al., the contents of which are incorporated herein by reference in their entirety.
Arcing in electrical equipment, e.g., from transformers in electrical cabinets, also produces ultrasonic signals that can be detected. Examples of this use can be found in U.S. Published Patent Application US2006/0209632-A of Goodman, the details of which are hereby incorporated herein by reference in their entirety. Both motors and electrical cabinets used in large facilities may be positioned at widely separated locations.
Since acoustic energy created by faulty bearings and discharging electrical components is both in the audible and ultrasonic frequency ranges, generally in the range of 40 kHz, in noisy audible industrial environments, the ultrasonic component is easily detected and located. Thus, means are typically provided for heterodyning, or demodulating, the detected signal into the audio range, and various schemes are available for doing this.
When using ultrasonic energy to detect leaks, worn bearings, electrical arcing or other malfunctions, it is useful to have a portable ultrasonic sensor which indicates the presence and intensity of ultrasonic energy both visually and audibly. U.S. Pat. No. Re. 33,977 to Goodman et al. discloses an ultrasonic sensor that displays the intensity of the detected signal on an output meter operable in either linear or logarithmic mode, and also provides for audio output through headphones. U.S. Pat. No. 4,987,769 to Peacock et al. discloses an ultrasonic detector that displays the amplitude of the detected ultrasonic signal on a ten-stage logarithmic LED display. However, the detector disclosed in Peacock does not process the detected signal to produce an audible response, nor does it provide for signal attenuation after the initial pre-amplification stage.
A portable device which has been used in the past to detect ultrasonic energy is the UE 10,000 made by U.E. Systems of Elmsford, N.Y. This device is covered by U.S. Pat. No. 6,707,762, No. 6,804,992 and No. 6,996,030 to Goodman et al, which are incorporated herein by reference in their entirety. The UE 10,000 detects ultrasonic signals from worn bearings and converts the signals to the audio range. These signals can then be heard by an operator thought headphones as a way of detecting malfunctions. The audio signal can be saved and later downloaded to an external spectrum analyzer in order to make more precise determinations of the status of the bearings.
After extended use of the detection equipment, operators often tend to begin to use their ears as a guide to the condition of the motor bearings, as opposed to the amplitude readings on the LCD display of the device. However, it is extremely difficult for a person to discern with their ears the differences between inputs that are representative of bearings just beginning to become worn and those which are more seriously worn. The use of the human ear is a highly unreliable way in which to predict faults. By delivering the signal to an external spectrum analyzer, this can be overcome. The difficulty is that the motors with bearings under test can be spread out over large distances. By the time all of the motors have been surveyed, the portable detector has been returned to a maintenance facility and the stored heterodyned or audio signals are downloaded to a spectrum analyzer, bearings which are marginal may fail. Complete failure of the bearings can leave a motor inoperable for a period of time. In some instances, it is very detrimental to have a motor out of service for even a small amount of time, e.g., a cooling pump.
In addition to ultrasonic detection apparatus, the UE, 15000 also includes a camera with which images of the machine under test can be recorded. This is useful in locating and identifying a particular motor which has a bearing problem.
It would be advantageous if portable ultrasonic detectors had the on-board capability to perform spectrum analysis on received signals. This would eliminate the time delay between a reading and confirmation of the detection of an impending bearing fault.
Fault prediction can be based not only on the absolute value of a reading, but also on a comparison with a prior reading. For example, a good bearing may make an unusually large ultrasonic signal, but not be in a failure mode. If a consistent signal is detected over a long period of time there may be no need to take corrective action. However, if the level is increasing over time, it may be prudent to replace the bearing at the next convenient time. Thus, it would further be beneficial if the portable ultrasonic detector were to have an on-board recording and storage device that can be used to compare the current sound from the item under test, e.g., a bearing, with sounds recorded previously.